1. Field of the Invention
The invention relates generally to the field of diagnostics and detection. More particularly, the invention relates to low resource processors for assessing molecular interactions. Specifically, the invention relates to the use of devices containing multiple chambers separated by surface tension valves for the processing of microbeads having screening reagents attached thereto. The device permits assaying for the content of a wide variety of environmental and biological samples, including whole cells.
2. Description of Related Art
Recent research has focused on the development of nucleic acid-based detection for low resource settings (Niemz et al., 2011). Nucleic acid-based detection systems, such as quantitative PCR (qPCR), are particularly attractive technologies for detection of pathogens because of their sensitivity, specificity and relatively rapid time-to-answer. The effectiveness of PCR is dependent on both the quality and quantity of nucleic acid template (Beuselinck et al., 2005) and the absence of interferents (Radstrom et al., 2004). For example, carbohydrates, proteins, lipids or other unidentified interferents present in clinical samples have all been shown to inhibit PCR and produce false negatives (Monteiro et al., 1997; Wilson, 1997; Coiras et al., 2003). In addition to various interferents, patient samples also contain nucleases, which directly reduce the number of nucleic acid targets present (Wilson, 1997).
To minimize false negatives and maximize the efficiency of nucleic acid-based diagnostics, nucleic acids are extracted and concentrated into an interferent-free buffer prior to testing. Several solid phase extraction kits are commercially available to purify DNA or RNA from patient samples. Many of these kits rely on selective nucleic acid binding to silica-coated surfaces in the presence of ethanol and a chaotropic agent, such as guanidinium thiocyanate (GuSCN) (Avison, 2007; Yamada et al., 1990). These kits are not cost effective for low resource use and often require the use of specialized laboratory equipment, such as a robot or centrifuge, and trained technicians that are unavailable in a low resource setting.
Microfluidics is one promising format for low resource cell-based diagnostics. Recently, there has been a growing interest in expanding microfluidic technologies for sample preparation (Niemz et al., 2011; Price et al., 2009). Many of these devices are suitable for integrating with downstream nucleic acid amplification and detection technologies (Chen et al., 2010; Hagan et al., 2011). However, the small surface area of solid phase available for cell binding and the limited sample volume that can be flowed through the channels limit the total mass of material recovered (Niemz et al., 2011), and therefore negatively impact the limit of detection.
Similar issues relate to the testing for many species of interest, including proteins, lipids, carbohydrates, and whole cells. Therefore, a rapid, noninvasive diagnostic technology for the isolation of whole cells is desirable, especially in low resource environments. Such technology would allow for blood cell profiling and the isolation and detection of cells to aid in cancer detection and to monitor disease progression and response to therapy for diseases such as HIV.